Presentation Title

Presenter Information

Start Date

November 2016

End Date

November 2016

Location

HUB 302-43

Type of Presentation

Poster

Abstract

Iron is one of the most abundant elements on earth, and is recognized as an important cofactor in enzymes, assisting in the transfer of electrons during catalysis. Its transition states, Fe(III) and Fe (II), allow microorganisms to pass on electrons, formed from the oxidation of organic compounds or hydrogen gas, to the former state, reducing it to the latter and generating cellular energy. In this study, we explore a cryptic cycle in anoxic marine sediments involving microbes, iron, and sulfur-containing compounds. In this cycle, disulfides accept electrons from Fe-reducing bacteria, reducing the disulfides to thiols. These thiols then pass electrons onto Fe(III), creating Fe(II) and recycling the thiols back into disulfides. Thus, the interaction of bacteria with iron is indirect, and Fe reduction occurs abiotically. Here, we hypothesize a shift in the microbial community structure at the sediment depth layer where both Fe(II) and thiols are present. To test this hypothesis, we examined microbial community structure along vertical profiles of salt marsh sediment cores via DNA isolation, amplification of 16S rRNA gene fragments, and high-throughput amplicon sequencing. Shifts in 16S rRNA gene composition were analyzed relative to sediment iron species concentrations measured by electrochemical spectroscopy to infer the metabolic roles of the sediment microbial community. OTUs in classes of Flavobacteriia, Verrucomicrobiae, and Gammaproteobacteria, were shown to correlate significantly with geochemical presence of Fe species. Core S (negative control) was shown to be more sulfide-rich, while core C was shown to be more Fe-rich and microbially diverse. Changes in community compositions between cores reflect geochemical shifts, but metagenomic and metatranscriptomic analyses are necessary to directly link OTUs to this cryptic cycle.

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Iron is one of the most abundant elements on earth, and is recognized as an important cofactor in enzymes, assisting in the transfer of electrons during catalysis. Its transition states, Fe(III) and Fe (II), allow microorganisms to pass on electrons, formed from the oxidation of organic compounds or hydrogen gas, to the former state, reducing it to the latter and generating cellular energy. In this study, we explore a cryptic cycle in anoxic marine sediments involving microbes, iron, and sulfur-containing compounds. In this cycle, disulfides accept electrons from Fe-reducing bacteria, reducing the disulfides to thiols. These thiols then pass electrons onto Fe(III), creating Fe(II) and recycling the thiols back into disulfides. Thus, the interaction of bacteria with iron is indirect, and Fe reduction occurs abiotically. Here, we hypothesize a shift in the microbial community structure at the sediment depth layer where both Fe(II) and thiols are present. To test this hypothesis, we examined microbial community structure along vertical profiles of salt marsh sediment cores via DNA isolation, amplification of 16S rRNA gene fragments, and high-throughput amplicon sequencing. Shifts in 16S rRNA gene composition were analyzed relative to sediment iron species concentrations measured by electrochemical spectroscopy to infer the metabolic roles of the sediment microbial community. OTUs in classes of Flavobacteriia, Verrucomicrobiae, and Gammaproteobacteria, were shown to correlate significantly with geochemical presence of Fe species. Core S (negative control) was shown to be more sulfide-rich, while core C was shown to be more Fe-rich and microbially diverse. Changes in community compositions between cores reflect geochemical shifts, but metagenomic and metatranscriptomic analyses are necessary to directly link OTUs to this cryptic cycle.